Laurence Berry's PhD research

I recently made some contributions to the discussion of fire refuges and their ecology in a new book addressing the recovery of Mountain Ash forests following the 2009 Black Saturday wildfires.

Here is the blurb from the publisher –

Mountain Ash draws together exciting new findings on the effects of fire and on post-fire ecological dynamics following the 2009 wildfires in the Mountain Ash forests of the Central Highlands of Victoria. The book integrates data on forests, carbon, fire dynamics and other factors, building on 6 years of high-quality, multi-faceted research coupled with 25 years of pre-fire insights.

Topics include: the unexpected effects of fires of varying severity on populations of large old trees and their implications for the dynamics of forest ecosystems; relationships between forest structure, condition and age and their impacts on fire severity; relationships between logging and fire severity; the unexpectedly low level of carbon stock losses from burned forests, including those burned at very high severity; impacts of fire at the site and landscape levels on arboreal marsupials; persistence of small mammals and birds on burned sites, including areas subject to high-severity fire, and its implications for understanding how species in this group exhibit post-fire recovery patterns.

With spectacular images of the post-fire environment, Mountain Ash will be an important reference for scientists and students with interests in biodiversity, forests and fire.

Aims: To identify which attributes of fire regimes affect temporal change in the presence and abundance of native mammals

Study area: Booderee National Park, south-eastern Australia

Methods: Our study was underpinned by time series data on 11 mammal species at 97 long-term sites between 2003 and 2013. We employed AIC-based selection of hurdle models to explore how temporal aspects of fire regimes influenced both the presence and the conditional abundance of a species at a site. The three key fire regime components examined were: (i) severity of a major fire in 2003, (ii) the interval between the 2003 fire and the previous fire, and, (iii) number of past fires – a reflection of the fire history at a site. The unique nature of our long term dataset enabled us to quantify the interactions between survey year and each of these three fire regime variables, an important aspect of ecological relationships missing from temporally-restricted studies.

Key findings:We found that multiple aspects of fire regimes influenced temporal variation in the presence and abundance of mammals. The best models indicated that 6 of the 11 species responded to two or more fire regime variables, with terrestrial rodents and the Long-nosed Bandicoot influenced by all three fire regime attributes. Almost all species responded to time since fire, either as an interaction with survey year or as a main effect. Fire severity or its interaction with survey year was important for most terrestrial rodents, the Long-nosed Bandicoot, and Common Ringtail Possum. Further complexity emerged through differences in the presence/absence versus the conditional abundance components of the hurdle models we constructed for each mammal species. The number of fires at a site was significant for species of terrestrial rodent (but not the eastern Chestnut Mouse), the Long-nosed Bandicoot, Common Ringtail Possum, and the Eastern Grey Kangaroo. Our findings contain evidence of the effects on native mammals of heterogeneity in fire regimes. They also strongly suggest that the invisible mosaic (sensu (Bradstock et al. 2005)) will have a large influence on the response of species to the next fire at a given site.

Implications:Temporal response patterns of mammal species were influenced by multiple fire regime attributes, and often in conjunction with survey year. This underscores the critical importance of long-term studies of biota that are coupled with datasets characterized by carefully documented fire history, severity and frequency. Long-term studies are essential to predict animal responses to future fires and guide future management such as when and where more (prescribed) fires are needed or, conversely, where and when long unburned vegetation is required. The complexity of observed responses highlights the need for large reserves in which patterns of heterogeneity in fire regimes can be sustained in both space and over time. Conservation managers also need to be cognisant of the effects on biota of some variables that are indirectly related or unrelated to fire.

Following a visit to the US last year and meeting Chad Hanson and Dominick Dellasala as part of a study into the use of ecological knowledge in fire management, I was invited to contribute chapters to their recent book on the Ecological importance of mixed severity fires. The book is expected to be published in June 2015.

The increasing frequency of large, high-severity fires threatens the survival of old-growth specialist fauna in fire-prone forests. Within topographically diverse montane forests, areas which experience less severe or fewer fires compared with those prevailing in the landscape may present unique resource opportunities enabling old-growth specialist fauna to survive. Statistical landscape models which identify the extent and distribution of potential fire refuges may assist land managers to incorporate these areas into relevant biodiversity conservation strategies.

We used a case study in an Australian wet montane forest to establish how predictive fire simulation models can be interpreted as management tools to identify potential fire refuges. We examined the relationship between the probability of fire refuge occurrence as predicted by an existing fire refuge model and fire severity experienced during a large wildfire. We also examined the extent to which local fire severity was influenced by fire severity in the surrounding landscape. We used a combination of statistical approaches including generalised linear modelling, variogram analysis and receiver operating characteristics and area under the curve analysis (ROC AUC).

We found that the amount of unburnt habitat and the factors influencing the retention and location of fire refuges varied with fire conditions. Under extreme fire conditions, the distribution of fire refuges was limited to only extremely sheltered, fire-resistant regions of the landscape. During extreme fire conditions, fire severity patterns were largely determined by stochastic factors that could not be predicted by the model. When fire conditions were moderate, physical landscape properties appeared to mediate fire severity distribution.

Our study demonstrates that land managers can employ predictive landscape fire models to identify the broader climatic and spatial domain within which fire refuges are likely to be present. It is essential that within these envelopes, forest is protected from logging, roads and other developments so that the ecological processes related to the establishment and subsequent use of fire refuges are maintained.

Summary

1. Mitigating the impacts of large-scale fires on biodiversity is becoming increasingly important as their frequency increases. In response, fire managers have engaged with the concept that retaining small unburnt residual areas of vegetation within extensively burnt landscapes may facilitate biodiversity conservation. However, it remains uncertain how the size and isolation of these unburnt residuals influence faunal distributions, persistence and recovery following fire.

2. We used a replicated observation study to test bird responses to the size and isolation of unburnt residuals in a Mallee woodland area recently burnt by a 28,000-ha wildfire in southern Australia. The scale of our study provided a rare opportunity to consider the responses of large mobile organisms to fire-induced habitat fragmentation. Within five replicated spatial blocks, we crossed two levels of isolation with large (5–7ha) and small (1–3ha) unburnt patches and matrix sites burnt five years previously. We compared these site types to six continuous (non-fragmented) unburnt sites. We surveyed each site on eight occasions.

3. Most birds occurred more frequently in unburnt habitat beyond the extent of the fire. Bird responses to the availability and spatial distribution of unburnt remnants within the fire were largely influenced by their ability to use the recently burnt matrix. Occurrence of five species was higher in unburnt residuals when more of the landscape within 500 m was burnt.

4. A fire refuge effect may be likely for two competitive species that occurred more frequently in unburnt residuals than in the burnt matrix or continuous unburnt habitat. For the weebill, re-colonisation following fire was likely to occur gradually over-time from ex-situ sources.

5. Synthesis and applications. To maintain avian diversity in fire-prone landscapes, our results suggest a need to shift management focus from creating networks of small unburnt patches, towards preserving large, intact areas of habitat. However, five species common to the burnt matrix preferentially selected residual patches when unburnt resources were locally scarce. Therefore, to benefit birds, land managers should limit the extent of applied burns and use narrow burns. When planning large burns, practitioners should consider that a number of species will remain absent from the landscape for several decades.

We examined the potential conservation value of topographic fire refuges for arboreal marsupials in a stand-replacing crown-fire forest ecosystem. We surveyed arboreal marsupial abundance across 48 sites in rainforest gullies burnt to differing extents by the 2009 fires in the Mountain Ash (Eucalyptus regnans) forests of the Victorian Central Highlands, Australia. The greater glider (Petauroides volans) was significantly less abundant within the extent of the 2009 fire. The mountain brushtail possum (Trichosurus cunninghami) appeared to be more abundant within the extent of the 2009 fire and was particularly abundant within unburnt peninsulas protruding into burnt areas from unburnt edges. Our results indicate that while fire refuges are potentially important outcomes of large fires for some species; further research is required to address the mechanisms underpinning these response patterns.

As part of their undergraduate studies at the Fenner School, two of our volunteers have written short blogs about their experiences working with us in the field earlier this year. Our study greatly benefited from the help of these two enthusiastic and passionate students. It is great to see how their experiences in these forests have influenced their thinking on some of the key conservation issues facing the region.